The present invention relates to a motor-driven disk brake for vehicles that produces braking force by using a rotational torque generated from an electric motor. More particularly, the present invention relates to a motor-driven disk brake having an additional function to operate also as a parking brake.
A conventional motor-driven disk brake has a caliper body floatably supported on a carrier secured to a non-rotating part of a vehicle. The caliper body contains a piston, an electric motor, and a rotary-to-rectilinear motion converting mechanism for converting the rotation of the rotor of the motor into rectilinear motion and for transmitting it to the piston. A torque generated on the rotor by the operation of the electric motor is converted into thrust for the piston through the rotary-to-rectilinear motion converting mechanism to press brake pads against a disk rotor, thereby generating braking force.
In the motor-driven disk brake of the type described above, the pedal force or stroke applied to the brake pedal by the driver is detected with a sensor, and the rotation (rotational angle) of the electric motor is controlled according to the detected value, thereby obtaining desired braking force. In the event a failure occurs in the electrical system, it becomes impossible to brake the vehicle.
Accordingly, Japanese Utility Model Registration No. 2546348, for example, proposes a mechanical brake actuating mechanism in which a rotating shaft is connected to the above-described rotary-to-rectilinear motion converting mechanism through a clutch mechanism and a ball-and-ramp mechanism. When an external rotational force is applied to the rotating shaft by a lever operation, for example, the clutch mechanism is engaged through the ball-and-ramp mechanism to actuate the rotary-to-rectilinear motion converting mechanism, thereby generating braking force. The mechanical brake actuating mechanism is useful as a parking brake as well as effective as a safety measure in the event of a failure in the electrical system.
However, according to the mechanical brake actuating mechanism described in the above-mentioned gazette, the relationship between the braking force and the rotational angle (input angle) of the rotating shaft to which rotational force is externally inputted varies according to the piston position at the time of initiating an external operation (e.g. a lever operation). Accordingly, if the driver performs an external operation while stepping on the brake pedal, the input angle varies to a considerable extent according to the piston position, resulting in variations in the brake operating quantity. This causes the brake operating feeling to be degraded markedly. Conversely, if the brake pedal is stepped on in a state where the parking brake has been put in operation by an external operation, the motor-driven brake is unable to work because the rotary-to-rectilinear motion converting mechanism is operatively connected to an external operating member through the clutch mechanism. Consequently, the desired braking force cannot be obtained.
In addition, the external input transmitted to the piston is influenced by frictional force in the clutch mechanism and the rotary-to-rectilinear motion converting mechanism. Therefore, if the frictional force changes with time, braking force also changes. Consequently, it is difficult to obtain stable braking force for a long period of time.
The present invention was made to solve the above-described problems.
An object of the present invention is to provide a motor-driven disk brake capable of functioning as a parking brake satisfactorily without degrading the brake operating feeling and impairing the function of operating as a motor-driven brake and also capable of ensuring long-term braking stability.
The present invention provides a motor-driven disk brake having a pair of brake pads disposed at both sides, respectively, of a disk rotor. A piston is provided in a caliper body to face one of the pair of brake pads. A claw portion is provided on the caliper body to extend over the disk rotor so as to face the other of the pair of brake pads. The motor-driven disk brake further has an electric motor for rotating a rotor and a rotary-to-rectilinear motion converting mechanism for converting rotational motion of the rotor into rectilinear motion to move the piston forward or backward. A torque generated on the rotor by the operation of the electric motor is converted into thrust for the piston through the rotary-to-rectilinear motion converting mechanism to press the brake pads against the disk rotor, thereby generating braking force. The motor-driven disk brake has a rotation assisting device for transmitting an external input directly to the rotor to rotate the rotor through a predetermined angle in a direction such that the piston is propelled. The rotation assisting device allows the rotor to rotate in excess of the predetermined angle.
In the motor-driven disk brake arranged as stated above, the rotor is allowed to rotate freely in the direction such that the piston is propelled. Therefore, the externally applied brake operating quantity can be kept constant independently of the piston position. In addition, the function of operating as a motor-driven brake is ensured. Moreover, because the rotor is rotated directly by the rotation assisting device, it is possible to ignore friction variations in the rotary-to-rectilinear motion converting mechanism.
In addition, the present invention provides a motor-driven disk brake having a pair of brake pads disposed at both sides, respectively, of a disk rotor. A piston is provided in a caliper body to face one of the pair of brake pads. A claw portion is provided on the caliper body to extend over the disk rotor so as to face the other of the pair of brake pads. The motor-driven disk brake further has an electric motor for rotating a rotor and a rotary-to-rectilinear motion converting mechanism for converting rotational motion of the rotor into rectilinear motion to move the piston forward or backward. Further, the motor-driven disk brake has an operating member for parking and a rotation assisting device for allowing the rotor of the electric motor to be mechanically rotated by the operating member for parking. The rotation assisting device converts a torque generated on the rotor into thrust for the piston through the rotary-to-rectilinear motion converting mechanism to press the brake pads against the disk rotor, thereby generating braking force.